It is well known to harden steels by heat treatment at elevated temperatures under a carbon rich atmosphere followed by tempering at higher temperatures. During the heat treatment process iron carbide is formed at elevated concentrations. During tempering at still higher temperatures, the iron carbide dissolves and secondary metal carbides are formed. Such secondary metal carbides typically include carbides of molybdenum, chromium, vanadium and other alloy constituents in the steel. These secondary metal carbides provide enhanced hardness within the carburized zone of the steel part. In the past, the precipitation of secondary metal carbides has been promoted by the addition of cobalt to the steel. Specifically, the cobalt additions have resulted in the formation of nucleation sites to aid in the collection of the precipitating secondary metal carbides. While cobalt additions have been successful in promoting secondary carbide precipitation, the attendant cost of such additions has been burdensome.
In the past, copper has been added as a strengthening agent to steels such as HSLA alloys used in pipelines, ship hulls and the like where carbon contents must be kept at low levels generally below about 0.05 wt. %. It has been proposed that copper in these alloys has the further benefit of adding grain refinement and toughness. Copper has also been added in limited amounts to steels for corrosion resistance. It has also been found that copper acts as a heterogeneous nucleation site for other phases. Copper has also been added to medium carbon steels to counteract cyclic softening during fatigue.